Data smoother



June 1, 1954 P. A. NOXON EIAL 2,680,193

DATA SMOOTHER Filed June 17; 1950 nvi/e/vraes PAUL ANOXON ALF/FED ENNETTer 4 H fl wqzroklv Patented June 1, 1954 DATA SMOOTHER Paul A. Noxon,Tenafiy, N. J., and Alfred Bennett,

New York, N. Y.,

assignors to Bendix Aviation Corporation, Teterboro, N. J., acorporation of Delaware Application June 17, 1950, Serial No. 168,776

12 Claims.

The invention relates to data smoothing circuits, and more particularlyto data smoothing circuits responsive to relatively low frequencies.

Radio beams of the kind commonly used to guide an airplane automaticallyalong a predetermined fiight path usually include spurious informationcomprising undesirable voltages of relatively high frequencies, such asnoise and side bands generated in the ground transmitter. Also, the beamhas undesirable curves or bends be cause of reflection of the beam fromterrestrial objects or from aircraft flying in the vicinity of the beam.An airplane, automatically guided by an automatic pilot responsive tothe radio beam, responds to this spurious information and flieserratically. When the aircraft is cruising in response to the radio beamcontrol, the beam signal must be applied to the automatic pilot assmoothly as possible to provide a comfortable ride.

One object of the present invention is to eliminate the effects of thespurious information on the automatic pilot.

Another object is to smooth out minor variations in signal voltageswithout materially affecting the accuracy of the data representedthereby.

A further object is to provide a data smoothing circuit which is stable.

Another object is to provide a filter which passes signals of relativelylow frequencies with relatively small attenuation and effectivelyreiects signals of higher frequencies.

A further object is to provide an average signal by integrating thesignal voltage with a relatively long time constant so that the effectsof transients are eliminated.

Another object is to provide a smooth output voltage which does not havean undesirable time lag relative to the signal voltage.

The invention contemplates a data smoothing circuit for receiving avariable signal comprising a plurality of frequency components. Thedevice has a filter network with a relatively long time constant tointegrate the si nal. The integrated output voltage of the filter lagsbehind the signal determined by the time constant of the filter circuit.At relatively high frequencies, the actual time lag may be only a fewthousandths of a secand but at the low freuuencies contemplated by thepresent invention the delay may amount to several seconds. In fastflying aircraft, this slow response is undesirable. For this reason, theintegrated output of the filter is fed to a phase advancing network orrate circuit and the constants of the rate circuit may be selected sothat the resulting voltage is in phase with the original si nal or leadsthe original signal. The output of the rate circuit may be fed to aservo system and no undesirable delay in the response of the servosystem will be encountered.

The foregoing and other objects and advantages of the invention willappear more fully hereinafter from a consideration of the detaileddescription which follows, taken together with the accompanying drawingwherein one embodiment of the invention is illustrated. It is to beexpressly understood, however, that the drawing is for the purposes ofillustration and description only, and is not to be construed asdefining the limits of the invention.

In the drawing, the single figure is a wiring diagram of a novel datasmoothing circuit constructed according to the invention.

Referring now to the drawing for a more detailed description of thepresent invention, the novel data smoothing circuit is shown asincluding a filter network having an input transformer l with a primarywinding 3 adapted to receive a signal from a suitable source and with asecondary winding 5 connected to a grid 1 of a high gain amplifier tube9 and connected in series with the secondary l l of a feed-backtransformer 13 to ground. Cathode 15 of tube 9 is connected to groundthrough a cathode resistor 11.

Plate it of tube 9 is connected through a re sistor to a 13+ supply andthrough a condenser 2! to the grids 23, of a pair of discriminator tubes21, 29, respectively. Grids 23, 25 are connected to a negative C biasthrough a grid leak resistor 35. Cathodes 31, 33 of tubes 21, 29,respectively, are grounded.

Plates 31, 39 of tubes 21, 29 are connected to heater elements 41, 43,respectively, of a thermal time delay tube of the kind shown anddescribed in U. S. Patent No. 2,463, u d March 8, 1949 and assigned to acommon assignee. The heaters are connected to a suitable source ofalternating current supply 41 in phase with the modulated signalfrequency. The time delay tube includes a pair of resistors 49, 5! inheat exchange relation with heaters M, 43, respectively, and forming twoadjoining arms of a Wheatstone bridge circuit. The other two arms of thebridge circuit are formed by a center-tapped resistor 53 connectedacross alternating power source 41.

The primary winding of feed-back transformer 13 is connected across thebridge circuit to the center tap 51 of resistor 53 and between resistors49, 5|.

The arrangement above described corresponds generally to the circuitshown and described in co-pending application Serial No. 90,236, filedApril 20, 1949 and assigned to a common assignee.

The time delay tube may have any desired time constant to filter outundesirable voltages of predetermined frequencies. In one arrangement,the time delay tube has a time constant of two minutes and the circuitelfectively attenuates signals having frequencies above six cycles perminute. As mentioned above, such a delay between the incircuit includingresistors tegrated output of the filter circuit and the input signal isundesirable when the control device is used to operate an automaticpilot in an aircraft.

For this reason, the integrated signal across feed-back transformersecondary H is impressed on a phase advancing network or rate circuit,described below and closely resembling the filter network to provide aresulting signal corresponding to the integrated output of the filterand in phase with or leading the original signal as determined by thetime constant of the rate circuit.

Secondary winding 59 of a feed-back'transformer 6! has one end connectedbetween secondary windings and H of transformers l and I3 and has itsother end connected to a grid 65 of a high gain amplifier tube 65. Plate5? of tube 65 is connected to grids 89, H of a pair of discriminatortubes l3, l5 and the plates of the discriminator tubes are connected toheaters ll, E9 of time delay tube at. The output of tube 8!, asdetermined by unbalance of the associated bridge 83, 85 of tube 8! andcenter-tapped resistor 81, is impressed on the primary B9 of feed-backtransformer iii. The end of feed-back secondary 59 adjacent grid 53 maybe connected by a lead st to a rudder channel amplifier and an aileronchannel amplifier as described in the above co-pending applicationSerial No. 90,236, and provides a resulting signal in phase with orleading the original signal fed to transformer l. The time constant ofthe second time delay circuit preferably is greater than the timeconstant for the first time delay circuit so that even at such lowfrequencies as one cycle in five minutes the resulting signal will leadthe original signal.

When the device is used with an automatic pilot to guide an airplaneautomatically along a predetermined flight path, the modulated signalfrom a cross pointer meter may be used to energize winding 3 oftransformer l, but it should be understood that any amplitude modulatedsignal developed as a result of a variable condition or function beingconsidered may be used. The data smoothing circuit will respond tovariable a;

D. C. signals as well as amplitude modulated signals by substituting inplace of transformer l suitable D. C. components, such as a magneticamplifier of the kind described in co-pending application Serial No.165,508, filed June l, 1959 and assigned to a common assignee,

The input signal is amplified by amplifier tube 9 and discriminatedagainst by discriminator tubes 21, 29 and one or the other of theheaters 4|, mined by the phase of the signal relative to thediscriminator plate supply. The grids of the discriminator tubespreferably are biased so that the heater elements for zero signal inputare heated continuously at the midpoint of the useful range. Morecurrent flows in one heater element than in the other, and the bridge isunbalanced and a voltage is fed back to transformer 13. The integratedvoltage across secondary winding H of transformer l3 lags behind thesignal impressed on transformer l, but has undesirable frequencies andirregularities removed therefrom. The integrated voltage is amplified bytube 65 and is discriminated against by discriminator tubes 13, 15, andthe output of the discriminator is impressed on heaters H, 19 of timedelay tube 3!. The output of tube 81, as determined by unbalance of theassociated bridge circuit, is impressed on feed-back transformer 6 l.The resulting voltage appearing on grid 63 of amplifier tube 43 of timedelay tube 45 is heated as deteris the difference between the integratedvoltage and the feed-back voltage across transformer SI and is a ratesignal in phase with or leading the original signal. The resultingvoltage may be applied through lead 9! to a servo system or otherapparatus responsive thereto as shown and described in applicationSerial No. 90,236.

The data smoothing circuit includes a filter which passes signals ofrelatively low frequencies with relatively small attenuation andeffectively rejects signals of higher frequencies. The time lag ofthe'first time delay circuit, which normally attenuates frequenciesabove six cycles per minute, is effectively changed to a lead angle bythe phase advancing network.

Although the data smoothing circuit herein described is appliedspecifically to control of aircraft by a radio beam, it should beunderstood that the circuit may be applied to any servo system whichrequires a smooth signal in phase with or leading the original signal,and this is readily accomplished by selecting suitable time constantsfor the two time delay circuits to filter undesirable frequencies andprovide the necessary phase advance.

The data smoothing circuit described is especially adapted for passingfrequencies below three or four cycles per minute and for rejectinghigher frequencies, but as mentioned above, by selecting difierent timeconstants, other frequen cies can be made critical. Spurious informationis rejected and minor variations in the signal voltage are smoothed outwithout materially affecting the accuracy of the data represented by thesignal voltage. The circuit provides an average signal by integratingthe signal voltage so that the eifects of transients are eliminated andthe signal has a practical degree of smoothness.

Although but one embodiment of the invention has been illustrated anddescribed in detail, it is to be expressly understood that the inventionis not limited thereto. Various changes can be made in the design andarrangement of the parts without departing from the spirit and scope ofthe invention as the same will now be understood by those skilled in theart.

What is claimed is:

1. A data smoothing circuit adapted to receive a variable signal,comprising a filter network having a predetermined time constant forintegrating the signal, and a phase advancing network connected to thefilter network and receiving the integrated signal for having a time constant longer than said first-mentioned time constant for advancing thephase of the integrated signal and an output connected to said phaseadvancing network for utilizing the phase advanced integrated signal.

2. A data smoothing circuit adapted to receive a variable signal andcomprising a filter network having a thermal time delay device with arelatively long time constant for integrating the signal, and a phaseadvancing network connected to the filter network and receiving theintegrated signal and having a thermal time delay device with a timeconstant longer than the time constant of the first-mentioned thermaltime delay device for advancing the phase of the integrated signal andan output connected to said phase advancing network for utilizing thephase advanced integrated signal.

3. A data smoothing circuit adapted to receive a variable signal andcomprising a filter network for integrating the signal, and a phaseadvanch s network connected to the filter network and receiving theintegrated signal and advancing its phase, each of said networksincluding an input, a time delay device, and feed-back means connectingthe time delay device to the input of the associated network.

4. Structure as described in claim 3 in which the time delay device ofthe phase advancing network has a time constant longer than the timeconstant of the integrating network so that the phase advancedintegrated signal leads the variable signal.

5. In a device of the kind described for receiving a variable signal, afirst time delay circuit having a feed-back means for integrating thesignal, a second time delay circuit connected to said first time delaycircuit and having feed-back means, said second time delay circuitreceiving the integrated signal and taking the voltage difierencebetween the integrated voltage and the feed-back voltage of the secondtime delay circuit to provide a resulting signal substantially in phasewith the variable signal.

6. In a device of the kind described having an input for receiving avariable signal comprising a pair of components of difierentfrequencies, first time delay means connected to said input andresponsive to only one of said components, feed-back means connectingsaid time delay means and said input for cancelling said one componentat said input and providing an integrated signal, second time delaymeans having an input connected to said feed-back means for receivingthe integrated signal, and feed-back means connecting said second timedelay means and said last-mentioned input to provide a resulting signalsubstantially in phase with the variable signal.

7. In a device of the kind described having an input for receiving avariable signal comprising a pair of components of differentfrequencies, first means comprising a thermal time delay deviceconnected to said input and having a predetermined time constant so asto respond to only one of said components, feed-back means connectingsaid device and said input for cancelling said one component at saidinput and provid ing an integrated signal, second means having a secondinput connected to said feed-back means for receiving the integratedsignal and comprising a second thermal time delay device associated withsaid second input, second feed-back means connecting said second timedelay device and said second input for providing a resulting signal,said second time delay device having a predetermined time constant sothat the resulting signal is in phase with. or leads the variablesignal.

8. A device of the kind described including a low pass filter having aninput for receiving a variable signal comprising at least two componentsof different frequencies, means including a thermal time delay deviceassociated with said input and having a predetermined time constant soas to respond to only the lower frequency component and be unresponsiveto the higher frequency component to integrate the variable signal,means connecting said time delay device and said input for cancellingsaid lower frequency component at said input, means having a secondinput connected to said connecting means and including a second thermaltime delay device associated with said second input, means con- 6necting said second time delay device and said second input forproviding a resulting signal in phase with, or leading the variablesignal.

9. A device of the kind described including a low pass filter having aninput for receiving a variable signal comprising a pair of components ofdiiferent frequencies, an amplifier connected to said input forreceiving said components, means comprising a time delay deviceconnected to said amplifier and having a predetermined time constant soas to respond to only the lower frequency component to provide anintegrated signal, feed-back means connecting said input and said timedelay device for cancelling said lower frequency component, means havinga secand input connected to said feed-back means for receiving theintegrated signal and including a second amplifier connected to saidsecond input, a second time delay device connected to said secondamplifier, second feed-back means connecting said second input and saidsecond time delay device for providing a resulting signal, said secondtime delay device having a predetermined time constant so that theresulting signal is in phase with, or leads the variable signal.

10. A data smoothing circuit adapted to receive a variable signal andcomprising a source of reference voltage, a filter network operativelyconnected With said voltage source for integrating the signal andincluding a discriminator for comparing the signal with said referencevoltage to detect the phase of the signal, and a phase advancing networkconnected to the filter network and receiving the integrated signal andadvancing its phase.

11. A data smoothing circuit adapted to receive a variable signal andcomprising a source of reference voltage, a filter network forintegrating the signal, and a phase advancing network 0perativelyconnected to said filter network and said voltage source for receivingthe integrated signal and advancing its phase and including adiscriminator for comparing the signal with said reference voltage todetect the phase of the integrated signal.

12. A data smoothing circuit adapted to receive a variable signal andcomprising a filter network for integrating the signal and including adiscriminator to detect the phase of the signal, a source of referencevoltage, and a phase advancing network operatively connected to saidfilter network and said voltage source for receiving the integratedsignal and advancing its phase and including a discriminator forcomparing the signal with said reference voltage to detect the phase ofthe integrated signal.

References Cited in the file of this patent UNITED STATES PATENTS

